The present invention relates to a surveillance installation. In public places with a large through-flow of people TV cameras are generally used, connected to a surveillance centre where an observer sits and watches events. This is an efficient but extremely expensive method. For surveillance of areas where only a few people normally pass it is generally advisable to close off the area by means of a barrier or signs stating that entry is not permitted or is only permitted at certain times.
The present invention relates to an installation for surveillance of an area of the latter type. It is thus important that persons coming into contact with the installation are not in any way injured thereby. This is enabled by the invention by the provision of a manned or unmanned central unit which receives information if anyone is at the periphery of the area. The central unit is electrically connected to a number of sensing means located along the periphery of the area. Each sensing means is provided with one or more sensitive members which, when activated, alter the electrical state in the current circuit including the sensing means and said central unit. The sensitive member may constitute a wire, a net or the like which may either be placed on the surface of the ground or be suspended.
According to an advantageous embodiment the sensitive member is provided at one end with a magnet loosely applied on the sensing means and retained there by an attraction member which may consist of a strip of ferrometal. If the sensitive member is touched the magnet is easily dislodged and the electrical state in the above-mentioned current circuit is thus altered. Said magnet might, for instance, influence a circuit breaker or switch so that, in the absence of the magnet, a resistor is short-circuited.
It should be evident that the magnetic force of the magnet at the sensing means can be controlled by varying the distance between the magnet and the unit in the sensing means to which the magnet is attracted.
Electric current is transmitted between the central unit and a sensing means through a two-way wire. Both direct and alternating current are suitable for the purpose.
According to an advantageous embodiment of the present invention the installation can also be used to initiate action members of various types. Such action members may consist of a tape-recorder providing information as to the cause of the trespassing. Other examples of action members are search-lights or a unit emitting a smoke screen. For military applications the action member may consist of a mine or a unit emitting toxic gas.
To enable the installation to be used for both gathering information and taking action it is advisable to use two different direct voltages. The same wire connections used for the sensing means can then also be used for the action members. Each sensing means, and possibly also the central unit, should include a rectifier. This enables the two direct voltages to be pole-inverted with respect to each other, one direct voltage only cooperating with the sensing member and the other direct voltage only cooperating with the action member.
The two direct voltages may have the same or different values. In some cases it has proven advisable for one voltage to have a low value and the other a high value.
Further characteristics of the present invention are revealed in the following claims.
The present invention will be described in more detail with reference to the accompanying drawings showing one embodiment thereof.